Problem: Solve for $x$ and $y$ using substitution. ${x+2y = -4}$ ${x = -y-5}$
Explanation: Since $x$ has already been solved for, substitute $-y-5$ for $x$ in the first equation. ${(-y-5)}{+ 2y = -4}$ Simplify and solve for $y$ $-y-5 + 2y = -4$ $y-5 = -4$ $y-5{+5} = -4{+5}$ ${y = 1}$ Now that you know ${y = 1}$ , plug it back into $\thinspace {x = -y-5}\thinspace$ to find $x$ ${x = -}{(1)}{ - 5}$ $x = -1 - 5$ ${x = -6}$ You can also plug ${y = 1}$ into $\thinspace {x+2y = -4}\thinspace$ and get the same answer for $x$ : ${x + 2}{(1)}{= -4}$ ${x = -6}$